The subject matter herein relates generally to expanded beam connectors that change a mode field diameter of propagating light to couple an optical fiber to another optical element.
It is often necessary to optically couple discrete optical elements. For example, an optical cable may include a bundle of optical fibers and may be configured to mate with an optical device (or other optical cable). The cable and device may be configured such that the end of each optical fiber aligns with a corresponding optical element of the device. The optical element may include, for example, a lens or another optical fiber. Two common methods for optically coupling discrete optical elements include physical contact coupling and expanded beam (EB) coupling. When coupling separate optical fibers through physical contact, a ferrule is attached to the end of each optical fiber. The ferrule includes an optical path that extends from the core of the optical fiber to a polished face of the ferrule. Both ferrules are inserted into a common sleeve that aligns the ferrules. The polished faces of the ferrules abut each other within the common sleeve thereby optically coupling the optical fibers. As such, physical contact coupling may also be referred to as butt coupling.
In EB coupling, the mode field diameter of the propagating light is expanded before traveling between the optical fiber and the other optical element. For example, an EB connector may include a lens structure (e.g., ball lens or molded lens) that has a fixed position relative to the end of the optical fiber. In some applications, two EB connectors optically couple to each other. The lens structure of a first EB connector receives light from an optical fiber and expands and collimates the light. This collimated light travels across a gap and is received by the lens structure of a second EB connector. The gap between the lens structures may include empty space or a material having predetermined optical properties. The lens structure of the second EB connector converges the light into another optical fiber to which the second EB connector is connected.
Both types of coupling (physical contact and EB) may perform sufficiently for some applications, but each has its drawbacks or challenges in implementation. Optical fibers that are coupled through physical contact may become misaligned and/or damaged when exposed to vibrations and/or substantial changes in temperature. More specifically, the material of the ferrules or sleeve may expand or contract causing the optical fibers to become misaligned. For applications that have a relatively small mode field diameter, such as the mode field diameters in single mode fibers, any dust that exists between the polished faces of the ferrules can scratch or damage the polished faces and/or block light through the optical interface resulting in a decrease in performance.
Although the EB connectors may be used with smaller optical fibers (e.g., single mode fibers) and in harsher environments, the technology can be relatively expensive. For instance, known EB connectors utilize ball lenses that have relatively small diameters (e.g., 1.0 mm, 0.1 mm, or smaller). It can be difficult and costly to manufacture, polish, and accurately position the ball lens in front of the fiber end. Other EB connectors utilize a molded lens. These lenses, however, can also be expensive to manufacture. In some cases, the molded lenses may not be suitable for harsher environments, such as those experienced in military applications.
Accordingly, there is a need for an EB connector that is less costly and/or capable of being used in harsher environments than known EB connectors.